The Vimeo clip has a lot of double-exposures / dissolves in them, so some of the flaring is just some out of focus light in one image layered over another image.

The first clip above has more flares & fogging from roll-outs and letting light leak through the eyepiece and by opening the camera door now & then, though I suppose these days there is a post tool to simulate that effect.

Shoot a lot of 16mm daylight spools in an ARRI-S and let light leak often through your eyepiece, and by opening the side door now & then and by reloading in bright light... you'll get a lot of that effect!